Method of manufacturing a bearing unit, and a motor having loaded thereon the bearing unit

ABSTRACT

A bearing unit includes an indent portion arranged on a portion of an inner circumferential surface of a housing to receive an oil supplying component. When inserting the oil supplying component, which is bent into a substantially round shape, a distance between a central axis of the housing and a center point of the inner circumferential surface of the substantially round-shaped oil supplying component is shorter than a radius of the inner circumferential surface of the housing. As a result of this unique arrangement, the inner circumferential surface of the oil supplying component securely makes contact with an outer circumferential surface of a sleeve of the bearing unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a bearing unit having a long operating life, and to a motor including such a bearing unit.

2. Description of the Related Art

An operating life of a bearing unit is an important element determining a length of an operating life of a motor having therein the bearing unit. Therefore, when oil runs out (e.g., by evaporation) of a bearing made of a sintered material impregnated with oil, the bearing unit will no longer operate. Thus, conventionally, a component for supplying oil has been used in order to extend the operating life of the bearing unit.

A long operating life is required for a motor used for a projector device (e.g., front-projection television, or rear-projection television) having applied therein DLP (Digital Light Processing) technology. Also, since the aforementioned projector device is sometimes operated continuously for a long period of time, the temperature inside the projector device may increase, thereby evaporating the oil impregnated in the bearing. Also, even when the aforementioned component for supplying oil is used, a secure contact has to be made between the component and the bearing in order for the component to supply oil to the bearing in an appropriate manner. If a secure connection is not made, the operating life of the bearing unit will not be extended, and thus the motor having therein such a bearing unit will not have a long operating life.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing a bearing unit in which a bearing and an oil supplying component are properly arranged with respect to each other. The bearing unit manufactured by a method according to a preferred embodiment of the present invention achieves a long and stable operating life. The preferred embodiments of the present invention also provide a motor including therein the bearing unit manufactured in accordance with the aforementioned method.

According to a preferred embodiment of the present invention, an oil supplying component makes contact with an outer circumferential surface of the sleeve so as to supply oil to the sleeve in an adequate manner. To be more specific, a distance between a central axis and a most curved portion of the oil supplying component, which is roundly bent to have a “c” shape, is designed to be shorter than a radius of an inner circumferential surface of a housing of the bearing unit such that the oil supplying component is operable to supply the oil effectively.

Other features, elements, steps, processes, characteristics and advantages of the present invention will become more apparent from the following description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a projector device.

FIG. 2 is a schematic cross sectional view of a motor according to a preferred embodiment of the present invention.

FIG. 3 is a schematic cross sectional view of a bearing unit according to a preferred embodiment of the present invention.

FIGS. 4A to 4C are schematic cross sectional views of oil supplying members according to various preferred embodiments of the present invention.

FIG. 5 is a schematic cross sectional view of a bearing unit according to yet another preferred embodiment of the present invention.

FIG. 6 is a schematic diagram showing a step of a method for manufacturing the bearing unit according to a preferred embodiment of the present invention.

FIG. 7 is a schematic diagram showing a step S1 of a method for manufacturing the bearing unit according to a preferred embodiment of the present invention.

FIG. 8 is a schematic diagram showing a step S2 of a method for manufacturing the bearing unit according to a preferred embodiment of the present invention.

FIG. 9 is a schematic diagram showing a step S3 of a method for manufacturing the bearing unit according to a preferred embodiment of the present invention.

FIG. 10 is a schematic diagram showing a step S4 of a method for manufacturing the bearing unit according to a preferred embodiment of the present invention.

FIG. 11 is a schematic diagram showing a step S5 of a method for manufacturing the bearing unit according to a preferred embodiment of the present invention.

FIG. 12 is a diagram showing a cross sectional view along line x-x in FIG. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that reference numerals, figure numbers, and supplementary explanations are provided for assisting the reader in finding corresponding components in the description of the preferred embodiments below to facilitate the understanding of the present invention. It is understood that these expressions are in no way intended to limit the scope of the invention.

Structure of the DLP Projector Device

FIG. 1 is a schematic diagram showing an entire structure of a display unit according to a preferred embodiment of the present invention. The display unit is a projector device 1 having applied therein DLP technology.

The projector device 1 includes a color wheel assembly 3 in which a disc shaped color wheel 2 is attached to a rotor portion of a motor 3 a, a light source 4 emitting an optical light toward the color wheel 2, a digital micro mirror device 5 (hereinafter, referred to as DMD 5) reflecting the optical light passing through the color wheel 2, and a projection optical system 6 projecting the optical light from the DMD 5 to a predetermined screen 7.

The color wheel 2 has, for example, three equal amount of areas each representing a color (e.g., red (R), green (G), and blue (B)) and each having a filter allowing an optical light to pass therethrough. The color wheel 2 rotates, due to the motor 3 a, at about 7200 rpm to about 14000 rpm. The DMD 5 provides in a two dimensional manner a plurality of micro reflection mirrors whose tilt can be adjusted. Once the optical light passes through the color wheel 2, the optical light having a predetermined frequency is transmitted in accordance with the frequency to predetermined reflection mirrors via a focusing lens 8. Then, the optical light will be reflected to the projection optical system 6 or to a predetermined position in accordance with the tilt of each reflection mirror. Then, only the optical light that enters the projection optical system 6 will be projected onto the screen 7. At this point, in accordance with an external signal, the tilt of each reflection mirror is adjusted with respect to the rotation of the color wheel 2. By this, the projector device 1 projects an image (e.g., R image, G image, and/or B image) in accordance with the external signal, thereby projecting a color moving image on the screen 7.

Structure of the Motor

Next, the entire structure of the motor provided with the color wheel assembly 3 will be described with reference to FIG. 2. FIG. 2 is a schematic cross sectional view of the motor according to a preferred embodiment of the present invention.

According to FIG. 2, the motor includes a rotor portion 10 which rotates about a central axis J1, a bearing portion 20 which supports the rotor portion 10 such that the rotor can freely rotate, and a stator portion 30 which retains the bearing portion 20.

The rotor portion 10 includes a shaft 11 which rotates about the same axis as the central axis J1, a rotor hub 12 which has attached thereto the color wheel 2 (not shown in FIG. 2) and which is affixed on a top portion of the shaft 11, a substantially cylindrically shaped yoke 13 which is made of a magnetic material and is affixed to the rotor hub 12, and a rotor magnet 14 which is affixed to the yoke 13.

The rotor hub 12 is made of a non magnetic material (e.g., aluminum). Also, the rotor hub 12 has a substantially cylindrical shape having an opening at a bottom portion thereof. An extension portion 12 b, which extends in a radially outward direction, is provided at a bottom portion of a cylinder portion 12 a. An attaching portion 12 b 1 is provided on a top surface of the extension portion 12 b. The color wheel 2 is to be attached to the attaching portion 12 b 1.

The yoke 13 is affixed to a lower portion of an outer circumferential edge of the extension portion 12 b by a desired fixing process (e.g., caulking). Also, the rotor magnet 14 is affixed by an adhesive, for example, to an inner circumferential surface of the yoke 13.

The bearing portion 20 includes a sleeve 21 which is made of a sintered material for rotatably supporting the shaft 11, a housing 22 which retains the sleeve 21, an oil supplying component 23 which is retained between the sleeve 21 and the housing 22 for supplying oil to the sleeve 21, a thrust plate 24 which is made of a resin material having superior abrasion resistance and rotatably supports a bottom portion of the shaft 11, and a substantially cup shaped lid portion 25 which retains the thrust plate 24.

The stator portion 30 includes a stator 31 which is affixed on an outer circumferential portion of the housing 22, a mounting board 32 which is affixed on a bottom surface of the housing 22, a circuit board 33 which is affixed on a bottom surface of the mounting board 32 for controlling rotation of the rotor portion 10, and a cable 34 which connects the stator portion 30 with an external power source (not shown in FIG. 2). Note that the cable 34 may be a Flexible Flat Cable (FFC) or a Flexible Printed Circuit (FPC).

The stator 31 includes a stator core 31 a which is formed by laminating a plurality of thin magnetic plates, and a coil 31 b coiling around the stator core 31 a. An end of the coil 31 b is electrically soldered to the circuit board 33.

An electric current coming from the external power source is conducted through the cable 34 to the stator 31 and generates a magnetic field around the stator 31. Due to an interaction between the generated magnetic field and the rotor magnet 14, the rotor portion 10 gains a rotary force.

Detailed Structure and Manufacturing Method of the Bearing Unit

1) Detailed Structure of the Bearing Unit

Next, a detailed structure and a manufacturing method of the bearing unit 20 a according to a preferred embodiment of the present invention will be described with reference to FIGS. 3 through 12. FIG. 3 shows a bearing unit 20 a. FIG. 4A shows the oil supplying component 23. FIG. 4B shows an element prior to being formed into the oil supplying component 23. According to FIG. 4B, the oil supplying component 23 has a stick shape. FIG. 4C also shows an element prior to being formed into the oil supplying component 23. According to FIG. 4C, the oil supplying component 23 has a ring shape. Note that the bearing unit 20 a includes the bearing portion 20 having inserted therein the shaft 11.

According to FIG. 3, the ring shaped indent portion 22 a which expands in a radial direction is provided on an upper portion of an inner circumferential surface of the housing 22. A top surface 22 a l of the indent portion 22 a forms an inclined surface wherein the surface extends in a radially upward and inward direction generating a tapered surface. Also, a bottom surface 22 a 2 of the indent portion 22 a defines, with respect to the central axis J1, a substantially perpendicular surface. Also, a ring shaped protruding portion 22 b is formed on a lower portion of an inner circumferential surface of the housing 22 which determines the axial position of the sleeve 21.

An upper side bearing 21 a and a lower side bearing 21 b are respectively provided on an upper portion and a lower portion on an inner circumferential surface of the sleeve 21. The upper side bearing 21 a and the lower side bearing 21 b have a slightly smaller diameter than the rest of the inner circumferential surface of the sleeve 21 so as to rotatably support the outer circumferential surface of the shaft 11. Also, the outer circumferential surface of the sleeve 21 makes contact with the inner circumferential surface of the housing 22 above and below the indent portion 22 a. Also, the oil supplying component 23 is located in a space generated between the indent portion 22 a and the outer circumferential surface of the sleeve 21. Also, a leveled portion 22 c is provided below the protruding portion 22 b. Also, a ring shaped plate 26 is provided below the protruding portion 22 b. Further, the lid portion 25 is affixed to a portion of a bottom surface of the leveled portion 22 c by a desired fixing process (e.g., caulking). At a top end of the lid portion 25, an upper end extension portion 25 a is arranged which extends in a radially outward direction. The plate 26 is secured between the upper end extension portion 25 a and the bottom surface of the protruding portion 22 b. Also, an oval shaped elevated portion 25 b is provided on an upward end surface of the lid portion 25. The thrust plate 24 is located on a top surface of the elevated portion 25 b.

The shaft 11 which will be inserted in the sleeve 21 has a substantially cylindrical shape. At a lower portion of the shaft 11, a reduced circumference portion 11 a is provided having a reduced circumference than the rest of the shaft 11. Further, a bottom end portion 11 b of the shaft 11 has a substantially circular arc shape. A tip portion at the end of the arc shape slides on the thrust plate 24, and is rotatably supported in the axial direction.

Also, an inner circumferential surface of the plate 26 is located closer to the central axis J1 than the inner circumferential surface of the protruding portion 22 b. Also, the inner circumferential surface of the plate 26 is located radially inwardly from the outer circumferential surface of the shaft 11, and radially outwardly from the outer circumferential surface of the reduced circumference portion 11 a. The protruding portion 22 b and the plate 26 define a mechanism to prevent the shaft 11 from coming out of the bearing unit.

At a top surface of the sleeve 21, a washer 27 is provided so that the oil which travels along the shaft 11 in an upward direction will be directed back to the sleeve 21.

According to FIG. 4A, the oil supplying component 23 whose axial position is determined by a position of the bottom surface 22 a 2 is a component made of a textile material (e.g., felt) which has been soaked with oil. According to FIG. 4B, the oil supplying component 23 is formed by cutting a strip of the textile material into a plurality of substantially quadrangular prism shaped bars. If the oil supplying component 23 is formed as shown in FIG. 4C in which a ring shaped component is cut out of the strip of the textile material, the rest of the strip will go to waste. That is, by forming the oil supplying component 23 having the substantially quadrangular prism shaped bars as shown in FIG. 4A, the material will be used efficiently. Also, since the textile material for the oil supplying component 23 is a flexible material, the bar shaped oil supplying component 23 can be roundly bent so as to form a “c” shape as shown in FIG. 4A.

Hereinafter, another preferred embodiment of the bearing unit will be described with reference to FIGS. 5 and 6. Note that in FIGS. 5 and 6, elements similar to those shown in FIG. 3 are denoted by similar reference numerals, and description thereof is omitted. Also, a housing shown in FIG. 5 will be denoted as housing 40, and that shown in FIG. 6 will be denoted as housing 50.

According to FIG. 5, the oil supplying component 23 is located axially lower than as shown in FIG. 3. When the oil supplying component 23 is located as shown in FIG. 5, a shape of the indent portion 41 of the housing 40 is such that a top surface of the indent portion 41 is substantially perpendicular with respect to the central axis J1, and a bottom surface of the indent portion 41 forms an inclined surface 41 b wherein the bottom surface extends in a radially downward and inward direction generating a tapered surface.

According to FIG. 6, the outer circumferential surface of the sleeve 21 makes contact with a lower portion of the inner circumferential surface of the housing 50 below the indent portion 51. Note that when the oil supplying component 23 is provided as shown in FIG. 5, the outer circumferential surface of the sleeve 21 makes contact with the inner circumferential surface of the housing 40 above the indent portion 41.

2) Manufacturing Method of the Bearing Unit 20 a

Next, a manufacturing method of the bearing unit 20 a will be described with reference to FIGS. 7 through 12. FIGS. 7 through 11 each show a schematic diagram illustrating a manufacturing step of the bearing unit 20 a. FIG. 12 is a diagram showing a cross sectional view of what is shown in FIG. 8 as viewed from a line x-x.

First, the oil supplying component 23 is inserted through an opening in the top surface 22 a 1 (see step S1 in FIG. 7). The oil supplying component 23 is roundly bent prior to being inserted. Due to the inclined surface formed at the top surface 22 a 1, the roundly bent oil supplying component 23 will be allowed to be restored within the indent portion 22 a. The aforementioned step S1 allows the oil supplying component 23 to be easily fixed at a predetermined axial position, thereby increasing an efficiency of the manufacturing process.

Next, after the oil supplying component 23 is inserted into the indent portion 22 a, oil is provided to the oil supplying component 23 (see step S2 in FIG. 8). Now, if the oil supplying component 23 is already soaked with oil prior to being inserted into the indent portion 22 a, the oil maybe spilled before insertion. An oil supplying component 23 not having an adequate amount of oil may shorten the operating life of the bearing unit. Therefore, it is important to insert the oil supplying component 23 which is not soaked with oil into the indent portion 22 a in order to prevent the aforementioned problem. The oil supplying component 23 can be ring shaped, for example.

According to FIG. 12, D1 which is a line connecting the central axis J1 and a center portion 23 b having the highest curvature in the roundly bent oil supplying component 23 is designed to be shorter than D2 which is a radius connecting the central axis J1 and a given point of an imaginary circle of the oil supplying component 23. As a result, a point on an inner circumferential surface of the oil supplying component 23 corresponding to the center portion 23 b makes contact with the outer circumferential surface of the sleeve 21. Also, since D1 is designed to be shorter than D2, H which is a radial thickness of the oil supplying component 23 preferably equals H2 which is a radial depth of the indent portion 22 a.

Also, once the oil supplying component 23 is placed inside the indent portion 22 a, a large restoring force will be applied on both ends of the roundly bent oil supplying component 23 while the smallest restoring force will be applied to the center portion 23 b. Hereinafter, a restoring force is a force acting upon the roundly bent oil supplying component 23, which is originally straight, so as to undo the bent shape. Due to the large restoring force, the inner circumferential surface of the center portion 23 b will be positioned closer to the central axis J1 than the inner circumferential surface of the housing 22.

Here, if H1, the thickness of the oil supplying component 23, is greater than the H2, the radial depth of the indent portion 22 a, the oil supplying component 23 will extend out of the indent portion 22 a and may be damaged when being inserted therein. Also, if H1 is smaller than H2, D1 may become greater than the D2, and therefore the oil will not be supplied in an adequate manner since the inner circumferential surface of the oil supplying component 23 and the outer circumferential surface of the sleeve 21 will not make contact with each other. Note that as long as H1 and H2 are designed to have an equal dimension, the dimensional tolerance will be varied only slightly.

Next, the sleeve 21 is inserted into and affixed in the housing 22 (see step S3 in FIG. 9). The sleeve 21 is inserted into the housing 22 by press fitting. Since the sleeve 21 is inserted into the housing 22 by press fitting, the inner circumferential surface of the housing 22 and the outer circumferential surface of the sleeve 21 make contact with each other such that the inner circumferential surface of the oil supplying component 23 and the outer circumferential surface of the sleeve 21 fittingly make contact with each other. An axial position of the sleeve 21 is determined in accordance with a position of a top surface of the protruding portion 22 b, and therefore, the axial position of the sleeve 21 is accurately determined.

Next, the plate 26, the thrust plate 24, and the lid portion 25 are affixed at the bottom portion of the housing (see step S4 in FIG. 10). In step S4, the plate 26 is provided on a bottom surface of the protruding portion 22 b. Then, the thrust plate 24 is placed on the top surface of the elevated portion 25 b. Then the lid portion 25 is affixed to the housing 22 by a desired fixing process (e.g., caulking).

Finally, the shaft 11 is inserted into the sleeve 21 (see step S5 in FIG. 11). The axial position of the shaft 11 is determined when the bottom end portion 11 b of the shaft 11 makes contact with the top surface of the thrust plate 24. An inner circumferential edge of the plate 26 is elastically deformed so as to allow the bottom end portion 11 b to pass therethrough. Then the shape of the inner circumferential edge of the plate 26 which is deformed when allowing the bottom end portion 11 b to pass therethrough is restored. As a result, a mechanism to prevent the shaft from coming off the bearing unit is provided.

The manufacturing method of the bearing unit as described above can be applied to the bearing unit as shown in FIGS. 5 and 6. Note, however, that according to FIG. 5, the bottom surface 41 b of the indent portion 41 is the tapered surface, and therefore, the oil supplying component 23 for the bearing unit as shown in FIG. 5 is inserted through a bottom portion of the bearing unit.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A manufacturing method of a bearing unit, the bearing unit comprising: a shaft; a sleeve made of a sintered material impregnated with oil, and having a substantially cylindrical shape and an inner circumferential surface arranged to rotatably support the shaft; a housing having an inner circumferential surface arranged to radially surround and support the sleeve, wherein the housing includes at the inner circumferential surface a ring shaped indent portion extending in a radially outward direction; and an oil supplying component retained in the indent portion and making contact with an outer circumferential surface of the sleeve so as to supply oil to the sleeve; wherein the manufacturing method of the bearing unit comprises the steps of: a) inserting the oil supplying component into the indent portion such that at least a portion of an inner circumferential surface of the oil supplying component is located closer to a central axis of the housing than an inner circumferential surface of the housing is to the central axis; b) inserting the sleeve into the housing; and c) inserting the shaft into the sleeve.
 2. The manufacturing method of the bearing unit according to claim 1, wherein the oil supplying component is made of a flexible material, and the oil supplying component is bent into a substantially round shape in step a) in order to be inserted into the indent portion.
 3. The manufacturing method of the bearing unit according to claim 1, wherein the oil supplying component is made of a textile material.
 4. The manufacturing method of the bearing unit according to claim 1, wherein at least one of a top surface and a bottom surface formed in a space between the inner circumferential surface of the housing and an inner circumferential surface of the indent portion includes an inclined surface extending in an axial direction.
 5. The manufacturing method of the bearing unit according to claim 2, further comprising soaking the oil supplying component with the oil after the step a).
 6. The manufacturing method of the bearing unit according to claim 2, wherein a center point along the inner circumferential surface of the substantially round-shaped oil supplying component is located closer to the central axis than the inner circumferential surface of the housing is to the central axis.
 7. The manufacturing method of the bearing unit according to claim 2, wherein a depth of the indent portion in a radial direction is substantially identical to a thickness of the oil supplying component.
 8. The manufacturing method of the bearing unit according to claim 2, wherein a gap is provided between an outer circumferential surface of the oil supplying component and the inner circumferential surface of the indent portion in the step a).
 9. The manufacturing method of the bearing unit according to claim 2, wherein a first end of the oil supplying component does not contact a second end of the oil supplying component when the oil supplying component is arranged in the indent portion.
 10. A motor having attached therein the bearing unit manufactured in accordance with claim 1, the motor comprising: a rotor portion affixed to one end of the shaft and having a rotor magnet; and a stator portion affixed to an outer circumferential surface of the housing and arranged to oppose the rotor magnet.
 11. The motor according to claim 10, wherein the rotor portion includes a color wheel mounted thereto.
 12. A manufacturing method of a bearing unit, the bearing unit comprising: a shaft; a sleeve made of a sintered material impregnated with oil, and having a substantially cylindrical shape and an inner circumferential surface arranged to rotatably support the shaft; a housing having an inner circumferential surface arranged to radially surround and support the sleeve, wherein the housing includes at the inner circumferential surface a ring shaped indent portion extending in a radially outward direction; and an oil supplying component retained in the indent portion and making contact with an outer circumferential surface of the sleeve so as to supply oil to the sleeve; wherein the manufacturing method of the bearing unit comprises the steps of: inserting the oil supplying component into the indent portion; inserting the sleeve into the housing such that at least one radius from a central axis of the housing to an inner circumferential of the oil supplying component is shorter than a radius from the central axis to an outer circumferential surface of the sleeve; and inserting the shaft into the sleeve.
 13. A motor having attached therein the bearing unit manufactured in accordance with claim 12, the motor comprising a rotor portion affixed to a first end of the shaft and having a rotor magnet, and a stator portion affixed on an outer circumferential surface of the housing and opposing the rotor magnet.
 14. The motor according to claim 13, wherein the rotor portion includes a color wheel attached thereto.
 15. A display unit comprising: a motor according to claim 10; a color wheel assembly including a rotary color wheel driven by the motor, the color wheel including color filters arranged to project and display a color picture image; a digital micro mirror device arranged to reflect a light transmitted through the color wheel by movable mirrors; a projection optical system arranged to project the light reflected from the digital micro mirror device onto a screen; and a case arranged to house the color wheel assembly, the light source, the digital micro mirror device, and the projection optical system.
 16. A display unit comprising: a motor according to claim 13; a color wheel assembly including a rotary color wheel driven by the motor, the color wheel including color filters arranged to project and display a color picture image; a digital micro mirror device arranged to reflect a light transmitted through the color wheel by movable mirrors; a projection optical system arranged to project the light reflected from the digital micro mirror device onto a screen; and a case arranged to house the color wheel assembly, the light source, the digital micro mirror device, and the projection optical system. 